FreeBSD Manual Pages

UNVIS(3) BSD Library Functions Manual UNVIS(3)
NAMEunvis, strunvis, strnunvis, strunvisx, strnunvisx -- decode a visual rep-
resentation of characters
LIBRARY
Standard C Library (libc, -lc)
SYNOPSIS#include <vis.h>
intunvis(char*cp, intc, int*astate, intflag);
intstrunvis(char*dst, constchar*src);
intstrnunvis(char*dst, size_tdlen, constchar*src);
intstrunvisx(char*dst, constchar*src, intflag);
intstrnunvisx(char*dst, size_tdlen, constchar*src, intflag);
DESCRIPTION
The unvis(), strunvis() and strunvisx() functions are used to decode a
visual representation of characters, as produced by the vis(3) function,
back into the original form.
The unvis() function is called with successive characters in c until a
valid sequence is recognized, at which time the decoded character is
available at the character pointed to by cp.
The strunvis() function decodes the characters pointed to by src into the
buffer pointed to by dst. The strunvis() function simply copies src to
dst, decoding any escape sequences along the way, and returns the number
of characters placed into dst, or -1 if an invalid escape sequence was
detected. The size of dst should be equal to the size of src (that is,
no expansion takes place during decoding).
The strunvisx() function does the same as the strunvis() function, but it
allows you to add a flag that specifies the style the string src is en-
coded with. Currently, the supported flags are: VIS_HTTPSTYLE and
VIS_MIMESTYLE.
The unvis() function implements a state machine that can be used to de-
code an arbitrary stream of bytes. All state associated with the bytes
being decoded is stored outside the unvis() function (that is, a pointer
to the state is passed in), so calls decoding different streams can be
freely intermixed. To start decoding a stream of bytes, first initialize
an integer to zero. Call unvis() with each successive byte, along with a
pointer to this integer, and a pointer to a destination character. The
unvis() function has several return codes that must be handled properly.
They are:
0 (zero) Another character is necessary; nothing has been recog-
nized yet.
UNVIS_VALID A valid character has been recognized and is available
at the location pointed to by cp.
UNVIS_VALIDPUSH A valid character has been recognized and is available
at the location pointed to by cp; however, the character
currently passed in should be passed in again.
UNVIS_NOCHAR A valid sequence was detected, but no character was pro-
duced. This return code is necessary to indicate a log-
ical break between characters.
UNVIS_SYNBAD An invalid escape sequence was detected, or the decoder
is in an unknown state. The decoder is placed into the
starting state.
When all bytes in the stream have been processed, call unvis() one more
time with flag set to UNVIS_END to extract any remaining character (the
character passed in is ignored).
The flag argument is also used to specify the encoding style of the
source. If set to VIS_HTTPSTYLE or VIS_HTTP1808, unvis() will decode URI
strings as specified in RFC 1808. If set to VIS_HTTP1866, unvis() will
decode entity references and numeric character references as specified in
RFC 1866. If set to VIS_MIMESTYLE, unvis() will decode MIME Quoted-
Printable strings as specified in RFC 2045. If set to VIS_NOESCAPE,
unvis() will not decode `\' quoted characters.
The following code fragment illustrates a proper use of unvis().
int state = 0;
char out;
while ((ch = getchar()) != EOF) {
again:
switch(unvis(&out, ch, &state, 0)) {
case 0:
case UNVIS_NOCHAR:
break;
case UNVIS_VALID:
(void)putchar(out);
break;
case UNVIS_VALIDPUSH:
(void)putchar(out);
goto again;
case UNVIS_SYNBAD:
errx(EXIT_FAILURE, "Bad character sequence!");
}
}
if (unvis(&out, '\0', &state, UNVIS_END) == UNVIS_VALID)
(void)putchar(out);
ERRORS
The functions strunvis(), strnunvis(), strunvisx(), and strnunvisx() will
return -1 on error and set errno to:
[EINVAL] An invalid escape sequence was detected, or the de-
coder is in an unknown state.
In addition the functions strnunvis() and strnunvisx() will can also set
errno on error to:
[ENOSPC] Not enough space to perform the conversion.
SEE ALSOunvis(1), vis(1), vis(3)
R. Fielding, RelativeUniformResourceLocators, RFC1808.
HISTORY
The unvis() function first appeared in 4.4BSD. The strnunvis() and
strnunvisx() functions appeared in NetBSD 6.0 and FreeBSD 9.2.
BUGS
The names VIS_HTTP1808 and VIS_HTTP1866 are wrong. Percent-encoding was
defined in RFC 1738, the original RFC for URL. RFC 1866 defines HTML
2.0, an application of SGML, from which it inherits concepts of numeric
character references and entity references.
BSD March 12, 2011 BSD